1. Field of the Invention
The present invention relates generally to an air-intake control system for a vehicular engine. More particularly, this invention pertains to an air-intake control system, which converts part of the flowing energy retained within the intake air into electric energy, and recovers this converted energy.
2. Description of the Related Art
A known air-intake system is disclosed in Japanese Unexamined Patent Publication No. 2-291426. This system is primarily designed for the purpose of reducing the pumping loss and improving the gas milage.
As shown in FIG. 18, the described system includes an engine 301 having a plurality of combustion chambers 302 (only one chamber is shown), which is communicated to a primary air-intake passage 303. A turbine (air motor) 304, which is rotated by the flow of intake air, is disposed midway along the passage 303. The turbine 304 is connected with a crank shaft 306, via a belt 305. The primary passage 303 has a secondary air-intake passage 307 for communicating the upper stream side with the downstream side with regard to the turbine 304. A first throttle valve 308 is provided within the primary passage 303. A second throttle valve 309 is provided within the secondary passage 306. Both throttle valves 308 and 309 are manipulated in relation to the degree of depression of the acceleration pedal 310.
When the engine 301 is operating in the low or light load, the second throttle valve 309 is completely closed, and the first throttle 308 is slightly opened. Therefore, all of the intake air is led to the turbine 304 through the passage 303. The intake air passed through the turbine 304 is introduced into the respective chamber 302, causing the turbine 304 to rotate. By this rotational motion, the flow energy of the intake air is partly recovered. In other words, torque generated by rotation of the turbine 304 is transmitted to a crank shaft 306, via the belt 305.
Therefore, when the engine 301 is operating with the low load, the engine 301 tends to have a pumping loss. However, this pumping loss is compensated by recovering the flowing energy of the intake air. Therefore, the gas milage is specifically improved, while the engine 301 is operating with low load.
However, according to this conventional system, the volume of intake air flowing into the respective combustion chamber 302 is controlled by the opening magnitude of each throttle valve 308 and 309. Therefore, when the degree of depression of the pedal 310 is small and the second throttle valve 309 is almost completely closed, almost all of the flowing energy of the intake air is consumed by the secondary throttle valve 309. In other words, the intake air flows into the respective chamber 302, through a small gap defined by the throttle valve 308. Furthermore, the intake air impinges against the secondary throttle valve 309. This impingement causes most of the flowing energy of the intake air to be consumed. Therefore, the turbine 304 is not substantially rotated, causing the energy recovery function to be lowered. This resultingly makes the flowing energy of the intake air difficult to recover in the wide range, in which the engine 301 is operating with the low load.